How to make project stock become valuated project stock

Hi Gurus,

I am basically From PP module. I have a query how to make project stock to valuated project stock with Valuation indicator M.

The issue is like  client is  doing production against WBS element , but they want to use Category MAT in settlement rule instead of WBS .By using this Category user getting error during GR like  "Valuation control in material master and special stock differs.

Please suggest how to resolve this issue.

Regards

Arabind